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Effect of irradiation on the composition and thermal properties of softwood kraft lignin and styrene grafted lignin
Author(s) -
Ayoub Ali,
Venditti Richard A.,
Jameel Hasan,
Chang HouMin
Publication year - 2014
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.39743
Subject(s) - lignin , softwood , styrene , grafting , irradiation , kraft paper , materials science , monomer , chemistry , molar mass distribution , hardwood , thermal stability , yield (engineering) , organic chemistry , chemical engineering , polymer chemistry , polymer , nuclear chemistry , copolymer , composite material , botany , physics , nuclear physics , engineering , biology
Lignin is an abundant, underutilized natural resource that has potential to be used as a biomaterial but is currently hampered in its use by not being uniform in structure and composition and is thermally unstable due to phenolic group. To address these issues and modify its thermal properties, softwood kraft lignin was modified using γ‐irradiation at low doses with and without styrene present and characterized. Irradiation of kraft lignin alone with γ‐radiation shows an initial decrease in molecular weight due to chain scission up to about 10 kGy followed by an increase in molecular weight due to crosslinking. NMR results indicate a decrease of about 15% in the OH content of the lignin with 30 kGy irradiation. Thermal properties such as T g , free volume and Δ C p follow accordingly. Irradiation at very low dosages was determined to facilitate the grafting of styrene monomer to lignin, decreasing the OH content by 23%. This effect increased the hydrophobicity of the material, depressed the value of T g , increased the Δ C p , increased the mobility in the liquid state, and made the material more thermally stable relative to the lignin alone, thus improving its processability at high temperatures. Both the irradiation of lignin alone and the grafting of styrene to lignin increased the yield of mass during pyrolysis and the activation energy for mass loss relative to untreated lignin alone. This work has demonstrated that the application of low dosages of γ‐irradiation is a promising method to attach functional molecules onto lignin for use in various applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131 , 39743.